Phytoplankton structure in different lake types in central Finland

Phyloplankton structure and its relation to physical and chemical properties of the water was studied in 58 central Finnish lakes. The biomass ranged from 0.2 to 14.2 g m −3 and the number of taxa per sample ranged from 33 to 152. The lakes were grouped into 5 types according to their trophic state: eutrophic, dyseutrophic, mesotrophic, oligotrophic, and acid oligotrophic lakes. The average biomass in eutrophic lakes was 5.57 g m −3 , in dyseutrophic 3.54 g m −3 , 1.23 g m −3 in mesotrophic, 0.52 g m −3 in oligotrophic and 0.39 g −3 in acid oligotrophic lakes. The average number of taxa per sample in the corresponding lake types were 109. 1, 79.3, 97.9, 90.9 and 43.8, respectively. The phytoplankton communities in eutrophic lakes were characterized by blue‐green algae (21.2% of total biomass) and green algae (18.7% of total biomass). In dyseutrophic lakes the proportion of green algae was much smaller (7.2% of total biomass) than in eutrophic lakes, whereas the proportion of diatoms and cryptophytes was higher (28.2 and 20.4% of total biomass, respectively). Chrysophytes dominated in the oligotrophic and mesotrophic lakes (27.3–39.9% of total biomass). The contribution of dinoflagellates to the total biomass was highest in the most oligotrophic acidified lakes and in those lakes the relative proportions of blue‐green and green algae were much higher than in the typical oligotrophic lakes. The lakes were also grouped into 8 community types according to the dominating algal group. Cyanophyceae‐ and Chlorophyceae‐types characterized the eutrophic lakes, whereas Chrysophyceae‐Dinopheceae‐type was typical for most oligotrophic lakes. The other 5 types occurred in mesotrophic and oligotrophic lakes but the physical and chemical properties of these lakes did not differ much.